Modeling of the Fe-Al phase diagram

Abstract

The thermodynamic models used to describe the Fe-Al phase diagram are studied in detail. We calculate the phase diagram of Fe-Al within the Bragg-Williams approximation and the tetrahedron approximation of the cluster-variation method, including nearest- and next-nearest-neighbor chemical and magnetic interactions. In contrast to previous calculations performed within the Bragg-Williams approximation, we find that the model does not reproduce the experimentally observed two-phase equilibrium region between a disordered Fe-Al solid solution and a paramagnetic B2 ordered phase. Within the model, the previously reported two-phase coexistence corresponds to metastable equilibrium. The equilibrium phase in that region of the phase diagram is a ferromagnetic B2 phase.